Hi – you can check the back issues of the American Harp Journal published by the American Harp Society – I remember that some years ago there was a very in-depth and detailed article with pictures concerning the whole process of gut string manufacture – There was also a video from Salvi about their harp manufacturing process which also included a section on gut string production – check with Salvi for the video – you might also write to Bow Brand strings, or any other major string manufacturer, and ask for information –
have fun –